With the development of the electronic industry, electronic products tend to be made small in size and with high performance, functionality and operating speed. In order to fabricate highly integrated and miniaturized semiconductor devices, a circuit board for carrying a plurality of active elements and circuits is gradually evolved from a double-layer board to a multi-layer board on which available circuit area is increased using the interlayer connection technology to accommodate a high density of integrated circuits in a limited space.
Conventional fabrication processes of a circuit board include performing a series of tests of electrical performance and mechanical strength on the circuit board after the circuit board is formed with circuits, and then providing a serial number or other relevant fabrication information on the circuit board for subsequent product tracing.
However, the above serial number or relevant fabrication information is formed by printing or laser as a pattern or mark on a surface of a solder mask layer of the circuit board when the circuit board is fabricated. Formation of such a pattern or mark cannot be performed inside the circuit board, and also increases the fabrication time and cost. Further, it may happen that the pattern or mark on the surface of the circuit board cannot be recognized or traced when an encapsulating process is carried out to encapsulate the circuit board for forming a semiconductor device.